Improvement of Thermoelectric Properties of p - and n -types Oxide Thick Films Fabricated by Electrophoretic Deposition
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1044-U09-01
Improvement of Thermoelectric Properties of p- and n-types Oxide Thick Films Fabricated by Electrophoretic Deposition Masayuki Sakurai1, Shigeru Horii1, Ryoji Funahashi2, Tetsuo Uchikoshi3, Tohru Suzuki3, Yoshio Sakka3, Hiraku Ogino1, Jun-ichi Shimoyama1, and Kohji Kishio1 1 Department of Applied Chemistry, University of Tokyo, Tokyo, 113-8656, Japan 2 National Institute of Advanced Industrial Science and Technology, Osaka, 363-8577, Japan 3 National Institute for Materials Science, Ibaraki, 305-0047, Japan ABSTRACT We report thermoelectric (TE) properties of mono-layer thick films of p-type [Ca2CoO3] CoO δ 0.62 2 (Ca349) and n-type compounds of Ca0.9La0.1MnO3 (Mn113) and LaNi0.98Mo0.02O3 (Ni113) for the improvement of TE performance in multi-layered TE modules. In the case of magnetically aligned Ca349 film, the improvement of TE properties due to the reduction of resistivity (ρ) was achieved by optimization of hot-pressing temperature and ρ was sensitive to relative density of the Ca349 layer. For the decrease in ρ of the n-type layers, two different approaches, the choice of Ni113 as a n-type compound and usage of fine powders of Mn113, were attempted. Both approaches were effective for reducing ρ even in the sintering at ~900°C.
INTRODUCTION Since the discovery of high thermoelectric (TE) performance of NaxCoO2 in single crystals[1], various TE oxides based on layered cobaltites such as [Ca2CoO3-δ]0.62CoO2 (Ca349)[2, 3] and [BiSrO]1.10CoO2[4](Bi222) were developed. Single crystals of these two cobaltites were reported to show high TE properties with practical dimensionless figure of merit of ZT (= S2Tρ-1κ-1 ; S : Seebeck coefficient, ρ : electrical resistivity, κ : thermal conductivity) > 1 at 700°C. These cobaltites showed highly chemical stability and are candidates of p-type TE materials for power generation using high temperature exhaust heat energy. On the other hand, CaMnO3[5], LaNiO3[6], and (ZnO)mIn2O3[7] were reported as n-type TE oxides. Especially, TE properties of CaMnO3 were enhanced by substitution of rare earth ions for Ca and ZT reached 0.16 for a Ca0.9Yb0.1MnO3 polycrystal at 1000 K[8]. The fabrication of TE module composed of the above TE oxides has been recently reported[9, 10] and was performed through a bulk process. The unicouple of TE module with ptype Ca349 and n-type Ca0.92La0.08MnO3 generated 63.5 mW/cm3 in a condition of ∆T = 390 K and Th = 773°C, where ∆T and Th are temperature difference between hot and cold sides and temperature at the hot side, respectively. As another approach, for the purpose of fabrication of downsized and highly integrated TE module, our group[11] reported the fabrication of a multilayered TE film composed of five layers of Al2O3 / magnetically grain-aligned (MA) Ca349 / Al2O3 / Ca0.9La0.1MnO3 (Mn113) / Al2O3 by electrophoretic deposition (EPD). Moreover, TE properties of a chip of TE module cut from the multi-layered thick film were also evaluated[12] and generated open-circuit voltage (V0) was ~90 mV at ∆T = 450°C and Th = 700°C. However, this T
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